Problem: Complete the equation. $\dfrac{4}{5} ~=~ $
Explanation: Let's figure out how many times we add $\dfrac{1}{5}$ to make $\dfrac{4}{5}$. $\dfrac{0}{5}$ $\dfrac{1}{5}$ $\dfrac{2}{5}$ $\dfrac{3}{5}$ $\dfrac{4}{5}$ $\llap{{+}}\!\frac{1}{5}$ $\llap{{+}}\!\frac{1}{5}$ $\llap{{+}}\!\frac{1}{5}$ $\llap{{+}}\!\frac{1}{5}$ $=\overbrace{{\dfrac1{5}} +{\dfrac1{5}} + {\dfrac1{5}} + {\dfrac1{5}}}^{{4}\text{ fifths}} $ $=\dfrac{{4}\times{1}}{{5}}$ $\dfrac{4}{5} = 4 \times \dfrac{1}{5}$